Two proposed improvements
If I could go back in time and advise Ormsby and Clark as they wee creating this strange, wonderful movie, I would have two major suggestions.
1. Make it obvious that certain characters (all?) were tripping harrrrrd on LSD. This goes hand in hand with the early 70s hippy/occult vibe and puts much of the dialogue in better perspective. I'm thinking of Anya's blathering about the beauty of the dead corpse followed by her freak out...
2. Turn it into a movie shoot instead of theatre troupe party. The pranks in the beginning would be filmed to get real reactions. The way it is, the only motivation the characters have is staisfying their *beep* boss's whims for an evening of "fun," but with Alan as a film director, they are there working, and may even be impressed with the method of his madness since it produced real shocks from them. They are more likely to be active participants in the silliness that eventually leads to their demise.